1. Field of the Invention
The present invention relates generally to methods and systems for patient anesthesia, and more particularly to methods and systems for the spinal delivery of anesthetics.
Spinal anesthetics are useful for many abdominal, pelvic, and lower extremity surgical procedures which require only local anesthesia. Spinal anesthesia is achieved by injecting a local anesthetic into the subarachnoid space between adjacent vertebrae in the lumbar region. While extremely useful, the effect and duration of spinal anesthesia is unpredictable and difficult to control.
Spinal anesthetics may be injected in a single dosage using a hypodermic syringe or may be administered in multiple dosages using a catheter which remains attached to the patient during the entire course of a surgical procedure. Such continuous administration of the spinal anesthetic helps assure extended anesthesia over longer periods of time. Heretofore, relatively large diameter catheters have been used for the continuous administration of spinal anesthetics. The large diameter, typically in the range from about 20 gauge to 24 gauge, has been employed primarily due to availability and ease of use. The use of larger diameter catheters, however, is undesirable since the larger diameter increases the chances of injury to the patient, particularly causing a greater incidence of postdural headaches.
For these reasons, it would be desirable to provide improved methods and systems for the continuous and intermittent administration of anesthetics to the subarachnoid space. In particular, it would be desirable to provide such methods and systems which permit continuous delivery of the anesthetic at relatively high injection rates without the need to introduce a relatively large diameter catheter to the subarachnoid space.
2. Description of the Background Art
Greene (1985) Anesth. Analg. 65:715-730, is a review article describing the effect of various factors on the distribution of spinal anesthetics in the subarachnoid space. In particular, the effect of the technique of injection is discussed on pp. 718-720.